Import tzcode 2022cvendor/tzcode/tzcode2022c

1 files changed, 1013 insertions, 467 deletions

diff --git a/zdump.c b/zdump.c
index 67bed06bc398..a63a3438f571 100644
--- a/zdump.c
+++ b/zdump.c
@@ -1,196 +1,344 @@
+/* Dump time zone data in a textual format.  */
+
 /*
 ** This file is in the public domain, so clarified as of
 ** 2009-05-17 by Arthur David Olson.
 */
 
-static char	elsieid[] = "@(#)zdump.c	8.10";
+#include "version.h"
 
-/*
-** This code has been made independent of the rest of the time
-** conversion package to increase confidence in the verification it provides.
-** You can use this code to help in verifying other implementations.
-*/
+#ifndef NETBSD_INSPIRED
+# define NETBSD_INSPIRED 1
+#endif
 
-#include "stdio.h"	/* for stdout, stderr, perror */
-#include "string.h"	/* for strcpy */
-#include "sys/types.h"	/* for time_t */
-#include "time.h"	/* for struct tm */
-#include "stdlib.h"	/* for exit, malloc, atoi */
-#include "float.h"	/* for FLT_MAX and DBL_MAX */
-#include "ctype.h"	/* for isalpha et al. */
-#ifndef isascii
-#define isascii(x) 1
-#endif /* !defined isascii */
+#include "private.h"
+#include <stdio.h>
+
+#ifndef HAVE_SNPRINTF
+# define HAVE_SNPRINTF (199901 <= __STDC_VERSION__)
+#endif
+
+#ifndef HAVE_LOCALTIME_R
+# define HAVE_LOCALTIME_R 1
+#endif
+
+#ifndef HAVE_LOCALTIME_RZ
+# ifdef TM_ZONE
+#  define HAVE_LOCALTIME_RZ (NETBSD_INSPIRED && USE_LTZ)
+# else
+#  define HAVE_LOCALTIME_RZ 0
+# endif
+#endif
+
+#ifndef HAVE_TZSET
+# define HAVE_TZSET 1
+#endif
 
 #ifndef ZDUMP_LO_YEAR
-#define ZDUMP_LO_YEAR	(-500)
+# define ZDUMP_LO_YEAR (-500)
 #endif /* !defined ZDUMP_LO_YEAR */
 
 #ifndef ZDUMP_HI_YEAR
-#define ZDUMP_HI_YEAR	2500
+# define ZDUMP_HI_YEAR 2500
 #endif /* !defined ZDUMP_HI_YEAR */
 
-#ifndef MAX_STRING_LENGTH
-#define MAX_STRING_LENGTH	1024
-#endif /* !defined MAX_STRING_LENGTH */
+#define SECSPERNYEAR	(SECSPERDAY * DAYSPERNYEAR)
+#define SECSPERLYEAR	(SECSPERNYEAR + SECSPERDAY)
+#define SECSPER400YEARS	(SECSPERNYEAR * (intmax_t) (300 + 3)	\
+			 + SECSPERLYEAR * (intmax_t) (100 - 3))
 
-#ifndef TRUE
-#define TRUE		1
-#endif /* !defined TRUE */
+/*
+** True if SECSPER400YEARS is known to be representable as an
+** intmax_t.  It's OK that SECSPER400YEARS_FITS can in theory be false
+** even if SECSPER400YEARS is representable, because when that happens
+** the code merely runs a bit more slowly, and this slowness doesn't
+** occur on any practical platform.
+*/
+enum { SECSPER400YEARS_FITS = SECSPERLYEAR <= INTMAX_MAX / 400 };
 
-#ifndef FALSE
-#define FALSE		0
-#endif /* !defined FALSE */
+#if !defined HAVE_GENERIC && defined __has_extension
+# if __has_extension(c_generic_selections)
+#  define HAVE_GENERIC 1
+# else
+#  define HAVE_GENERIC 0
+# endif
+#endif
+/* _Generic is buggy in pre-4.9 GCC.  */
+#if !defined HAVE_GENERIC && defined __GNUC__
+# define HAVE_GENERIC (4 < __GNUC__ + (9 <= __GNUC_MINOR__))
+#endif
+#ifndef HAVE_GENERIC
+# define HAVE_GENERIC (201112 <= __STDC_VERSION__)
+#endif
 
-#ifndef EXIT_SUCCESS
-#define EXIT_SUCCESS	0
-#endif /* !defined EXIT_SUCCESS */
+#if HAVE_GETTEXT
+# include <locale.h> /* for setlocale */
+#endif /* HAVE_GETTEXT */
 
-#ifndef EXIT_FAILURE
-#define EXIT_FAILURE	1
-#endif /* !defined EXIT_FAILURE */
+#if ! HAVE_LOCALTIME_RZ
+# undef  timezone_t
+# define timezone_t char **
+#endif
 
-#ifndef SECSPERMIN
-#define SECSPERMIN	60
-#endif /* !defined SECSPERMIN */
+#if !HAVE_POSIX_DECLS
+extern int	getopt(int argc, char * const argv[],
+			const char * options);
+extern char *	optarg;
+extern int	optind;
+#endif
+
+/* The minimum and maximum finite time values.  */
+enum { atime_shift = CHAR_BIT * sizeof(time_t) - 2 };
+static time_t const absolute_min_time =
+  ((time_t) -1 < 0
+   ? (- ((time_t) ~ (time_t) 0 < 0)
+      - (((time_t) 1 << atime_shift) - 1 + ((time_t) 1 << atime_shift)))
+   : 0);
+static time_t const absolute_max_time =
+  ((time_t) -1 < 0
+   ? (((time_t) 1 << atime_shift) - 1 + ((time_t) 1 << atime_shift))
+   : -1);
+static int	longest;
+static char *	progname;
+static bool	warned;
+static bool	errout;
 
-#ifndef MINSPERHOUR
-#define MINSPERHOUR	60
-#endif /* !defined MINSPERHOUR */
+static char const *abbr(struct tm const *);
+static intmax_t	delta(struct tm *, struct tm *) ATTRIBUTE_PURE;
+static void dumptime(struct tm const *);
+static time_t hunt(timezone_t, char *, time_t, time_t, bool);
+static void show(timezone_t, char *, time_t, bool);
+static void showextrema(timezone_t, char *, time_t, struct tm *, time_t);
+static void showtrans(char const *, struct tm const *, time_t, char const *,
+		      char const *);
+static const char *tformat(void);
+static time_t yeartot(intmax_t) ATTRIBUTE_PURE;
 
-#ifndef SECSPERHOUR
-#define SECSPERHOUR	(SECSPERMIN * MINSPERHOUR)
-#endif /* !defined SECSPERHOUR */
+/* Is C an ASCII digit?  */
+static bool
+is_digit(char c)
+{
+  return '0' <= c && c <= '9';
+}
 
-#ifndef HOURSPERDAY
-#define HOURSPERDAY	24
-#endif /* !defined HOURSPERDAY */
+/* Is A an alphabetic character in the C locale?  */
+static bool
+is_alpha(char a)
+{
+	switch (a) {
+	  default:
+		return false;
+	  case 'A': case 'B': case 'C': case 'D': case 'E': case 'F': case 'G':
+	  case 'H': case 'I': case 'J': case 'K': case 'L': case 'M': case 'N':
+	  case 'O': case 'P': case 'Q': case 'R': case 'S': case 'T': case 'U':
+	  case 'V': case 'W': case 'X': case 'Y': case 'Z':
+	  case 'a': case 'b': case 'c': case 'd': case 'e': case 'f': case 'g':
+	  case 'h': case 'i': case 'j': case 'k': case 'l': case 'm': case 'n':
+	  case 'o': case 'p': case 'q': case 'r': case 's': case 't': case 'u':
+	  case 'v': case 'w': case 'x': case 'y': case 'z':
+		return true;
+	}
+}
 
-#ifndef EPOCH_YEAR
-#define EPOCH_YEAR	1970
-#endif /* !defined EPOCH_YEAR */
+/* Return A + B, exiting if the result would overflow.  */
+static size_t
+sumsize(size_t a, size_t b)
+{
+  size_t sum = a + b;
+  if (sum < a) {
+    fprintf(stderr, _("%s: size overflow\n"), progname);
+    exit(EXIT_FAILURE);
+  }
+  return sum;
+}
 
-#ifndef TM_YEAR_BASE
-#define TM_YEAR_BASE	1900
-#endif /* !defined TM_YEAR_BASE */
+/* Return a pointer to a newly allocated buffer of size SIZE, exiting
+   on failure.  SIZE should be nonzero.  */
+static void * ATTRIBUTE_MALLOC
+xmalloc(size_t size)
+{
+  void *p = malloc(size);
+  if (!p) {
+    fprintf(stderr, _("%s: Memory exhausted\n"), progname);
+    exit(EXIT_FAILURE);
+  }
+  return p;
+}
 
-#ifndef DAYSPERNYEAR
-#define DAYSPERNYEAR	365
-#endif /* !defined DAYSPERNYEAR */
+#if ! HAVE_TZSET
+# undef tzset
+# define tzset zdump_tzset
+static void tzset(void) { }
+#endif
 
-#ifndef isleap
-#define isleap(y) (((y) % 4) == 0 && (((y) % 100) != 0 || ((y) % 400) == 0))
-#endif /* !defined isleap */
+/* Assume gmtime_r works if localtime_r does.
+   A replacement localtime_r is defined below if needed.  */
+#if ! HAVE_LOCALTIME_R
 
-#ifndef isleap_sum
-/*
-** See tzfile.h for details on isleap_sum.
-*/
-#define isleap_sum(a, b)	isleap((a) % 400 + (b) % 400)
-#endif /* !defined isleap_sum */
+# undef gmtime_r
+# define gmtime_r zdump_gmtime_r
 
-#define SECSPERDAY	((long) SECSPERHOUR * HOURSPERDAY)
-#define SECSPERNYEAR	(SECSPERDAY * DAYSPERNYEAR)
-#define SECSPERLYEAR	(SECSPERNYEAR + SECSPERDAY)
+static struct tm *
+gmtime_r(time_t *tp, struct tm *tmp)
+{
+  struct tm *r = gmtime(tp);
+  if (r) {
+    *tmp = *r;
+    r = tmp;
+  }
+  return r;
+}
 
-#ifndef HAVE_GETTEXT
-#define HAVE_GETTEXT 0
 #endif
-#if HAVE_GETTEXT
-#include "locale.h"	/* for setlocale */
-#include "libintl.h"
-#endif /* HAVE_GETTEXT */
 
-#ifndef GNUC_or_lint
-#ifdef lint
-#define GNUC_or_lint
-#else /* !defined lint */
-#ifdef __GNUC__
-#define GNUC_or_lint
-#endif /* defined __GNUC__ */
-#endif /* !defined lint */
-#endif /* !defined GNUC_or_lint */
+/* Platforms with TM_ZONE don't need tzname, so they can use the
+   faster localtime_rz or localtime_r if available.  */
 
-#ifndef INITIALIZE
-#ifdef GNUC_or_lint
-#define INITIALIZE(x)	((x) = 0)
-#else /* !defined GNUC_or_lint */
-#define INITIALIZE(x)
-#endif /* !defined GNUC_or_lint */
-#endif /* !defined INITIALIZE */
+#if defined TM_ZONE && HAVE_LOCALTIME_RZ
+# define USE_LOCALTIME_RZ true
+#else
+# define USE_LOCALTIME_RZ false
+#endif
 
-/*
-** For the benefit of GNU folk...
-** `_(MSGID)' uses the current locale's message library string for MSGID.
-** The default is to use gettext if available, and use MSGID otherwise.
-*/
+#if ! USE_LOCALTIME_RZ
 
-#ifndef _
-#if HAVE_GETTEXT
-#define _(msgid) gettext(msgid)
-#else /* !HAVE_GETTEXT */
-#define _(msgid) msgid
-#endif /* !HAVE_GETTEXT */
-#endif /* !defined _ */
+# if !defined TM_ZONE || ! HAVE_LOCALTIME_R || ! HAVE_TZSET
+#  undef localtime_r
+#  define localtime_r zdump_localtime_r
+static struct tm *
+localtime_r(time_t *tp, struct tm *tmp)
+{
+  struct tm *r = localtime(tp);
+  if (r) {
+    *tmp = *r;
+    r = tmp;
+  }
+  return r;
+}
+# endif
 
-#ifndef TZ_DOMAIN
-#define TZ_DOMAIN "tz"
-#endif /* !defined TZ_DOMAIN */
+# undef localtime_rz
+# define localtime_rz zdump_localtime_rz
+static struct tm *
+localtime_rz(timezone_t rz, time_t *tp, struct tm *tmp)
+{
+  return localtime_r(tp, tmp);
+}
 
-extern char **	environ;
-extern int	getopt(int argc, char * const argv[],
-			const char * options);
-extern char *	optarg;
-extern int	optind;
-extern char *	tzname[2];
+# ifdef TYPECHECK
+#  undef mktime_z
+#  define mktime_z zdump_mktime_z
+static time_t
+mktime_z(timezone_t tz, struct tm *tmp)
+{
+  return mktime(tmp);
+}
+# endif
 
-static time_t	absolute_min_time;
-static time_t	absolute_max_time;
-static size_t	longest;
-static char *	progname;
-static int	warned;
+# undef tzalloc
+# undef tzfree
+# define tzalloc zdump_tzalloc
+# define tzfree zdump_tzfree
+
+static timezone_t
+tzalloc(char const *val)
+{
+  static char **fakeenv;
+  char **env = fakeenv;
+  char *env0;
+  if (! env) {
+    char **e = environ;
+    int to;
+
+    while (*e++)
+      continue;
+    env = xmalloc(sumsize(sizeof *environ,
+			  (e - environ) * sizeof *environ));
+    to = 1;
+    for (e = environ; (env[to] = *e); e++)
+      to += strncmp(*e, "TZ=", 3) != 0;
+  }
+  env0 = xmalloc(sumsize(sizeof "TZ=", strlen(val)));
+  env[0] = strcat(strcpy(env0, "TZ="), val);
+  environ = fakeenv = env;
+  tzset();
+  return env;
+}
+
+static void
+tzfree(timezone_t env)
+{
+  environ = env + 1;
+  free(env[0]);
+}
+#endif /* ! USE_LOCALTIME_RZ */
+
+/* A UT time zone, and its initializer.  */
+static timezone_t gmtz;
+static void
+gmtzinit(void)
+{
+  if (USE_LOCALTIME_RZ) {
+    /* Try "GMT" first to find out whether this is one of the rare
+       platforms where time_t counts leap seconds; this works due to
+       the "Link Etc/GMT GMT" line in the "etcetera" file.  If "GMT"
+       fails, fall back on "GMT0" which might be similar due to the
+       "Link Etc/GMT GMT0" line in the "backward" file, and which
+       should work on all POSIX platforms.  The rest of zdump does not
+       use the "GMT" abbreviation that comes from this setting, so it
+       is OK to use "GMT" here rather than the more-modern "UTC" which
+       would not work on platforms that omit the "backward" file.  */
+    gmtz = tzalloc("GMT");
+    if (!gmtz) {
+      static char const gmt0[] = "GMT0";
+      gmtz = tzalloc(gmt0);
+      if (!gmtz) {
+	perror(gmt0);
+	exit(EXIT_FAILURE);
+      }
+    }
+  }
+}
 
-static char *	abbr(struct tm * tmp);
-static void	abbrok(const char * abbrp, const char * zone);
-static long	delta(struct tm * newp, struct tm * oldp);
-static void	dumptime(const struct tm * tmp);
-static time_t	hunt(char * name, time_t lot, time_t	hit);
-static void	setabsolutes(void);
-static void	show(char * zone, time_t t, int v);
-static const char *	tformat(void);
-static time_t	yeartot(long y);
+/* Convert *TP to UT, storing the broken-down time into *TMP.
+   Return TMP if successful, NULL otherwise.  This is like gmtime_r(TP, TMP),
+   except typically faster if USE_LOCALTIME_RZ.  */
+static struct tm *
+my_gmtime_r(time_t *tp, struct tm *tmp)
+{
+  return USE_LOCALTIME_RZ ? localtime_rz(gmtz, tp, tmp) : gmtime_r(tp, tmp);
+}
 
 #ifndef TYPECHECK
-#define my_localtime	localtime
+# define my_localtime_rz localtime_rz
 #else /* !defined TYPECHECK */
+
 static struct tm *
-my_localtime(tp)
-time_t *	tp;
+my_localtime_rz(timezone_t tz, time_t *tp, struct tm *tmp)
 {
-	register struct tm *	tmp;
-
-	tmp = localtime(tp);
-	if (tp != NULL && tmp != NULL) {
+	tmp = localtime_rz(tz, tp, tmp);
+	if (tmp) {
 		struct tm	tm;
 		register time_t	t;
 
 		tm = *tmp;
-		t = mktime(&tm);
-		if (t - *tp >= 1 || *tp - t >= 1) {
-			(void) fflush(stdout);
-			(void) fprintf(stderr, "\n%s: ", progname);
-			(void) fprintf(stderr, tformat(), *tp);
-			(void) fprintf(stderr, " ->");
-			(void) fprintf(stderr, " year=%d", tmp->tm_year);
-			(void) fprintf(stderr, " mon=%d", tmp->tm_mon);
-			(void) fprintf(stderr, " mday=%d", tmp->tm_mday);
-			(void) fprintf(stderr, " hour=%d", tmp->tm_hour);
-			(void) fprintf(stderr, " min=%d", tmp->tm_min);
-			(void) fprintf(stderr, " sec=%d", tmp->tm_sec);
-			(void) fprintf(stderr, " isdst=%d", tmp->tm_isdst);
-			(void) fprintf(stderr, " -> ");
-			(void) fprintf(stderr, tformat(), t);
-			(void) fprintf(stderr, "\n");
+		t = mktime_z(tz, &tm);
+		if (t != *tp) {
+			fflush(stdout);
+			fprintf(stderr, "\n%s: ", progname);
+			fprintf(stderr, tformat(), *tp);
+			fprintf(stderr, " ->");
+			fprintf(stderr, " year=%d", tmp->tm_year);
+			fprintf(stderr, " mon=%d", tmp->tm_mon);
+			fprintf(stderr, " mday=%d", tmp->tm_mday);
+			fprintf(stderr, " hour=%d", tmp->tm_hour);
+			fprintf(stderr, " min=%d", tmp->tm_min);
+			fprintf(stderr, " sec=%d", tmp->tm_sec);
+			fprintf(stderr, " isdst=%d", tmp->tm_isdst);
+			fprintf(stderr, " -> ");
+			fprintf(stderr, tformat(), t);
+			fprintf(stderr, "\n");
+			errout = true;
 		}
 	}
 	return tmp;
@@ -198,349 +346,399 @@ time_t *	tp;
 #endif /* !defined TYPECHECK */
 
 static void
-abbrok(abbrp, zone)
-const char * const	abbrp;
-const char * const	zone;
+abbrok(const char *const abbrp, const char *const zone)
 {
 	register const char *	cp;
-	register char *		wp;
+	register const char *	wp;
 
 	if (warned)
 		return;
 	cp = abbrp;
-	wp = NULL;
-	while (isascii((unsigned char) *cp) && isalpha((unsigned char) *cp))
+	while (is_alpha(*cp) || is_digit(*cp) || *cp == '-' || *cp == '+')
 		++cp;
-	if (cp - abbrp == 0)
-		wp = _("lacks alphabetic at start");
+	if (*cp)
+	  wp = _("has characters other than ASCII alphanumerics, '-' or '+'");
 	else if (cp - abbrp < 3)
-		wp = _("has fewer than 3 alphabetics");
+	  wp = _("has fewer than 3 characters");
 	else if (cp - abbrp > 6)
-		wp = _("has more than 6 alphabetics");
-	if (wp == NULL && (*cp == '+' || *cp == '-')) {
-		++cp;
-		if (isascii((unsigned char) *cp) &&
-			isdigit((unsigned char) *cp))
-				if (*cp++ == '1' && *cp >= '0' && *cp <= '4')
-					++cp;
-		if (*cp != '\0')
-			wp = _("differs from POSIX standard");
-	}
-	if (wp == NULL)
-		return;
-	(void) fflush(stdout);
-	(void) fprintf(stderr,
+	  wp = _("has more than 6 characters");
+	else
+	  return;
+	fflush(stdout);
+	fprintf(stderr,
 		_("%s: warning: zone \"%s\" abbreviation \"%s\" %s\n"),
 		progname, zone, abbrp, wp);
-	warned = TRUE;
+	warned = errout = true;
+}
+
+/* Return a time zone abbreviation.  If the abbreviation needs to be
+   saved, use *BUF (of size *BUFALLOC) to save it, and return the
+   abbreviation in the possibly-reallocated *BUF.  Otherwise, just
+   return the abbreviation.  Get the abbreviation from TMP.
+   Exit on memory allocation failure.  */
+static char const *
+saveabbr(char **buf, size_t *bufalloc, struct tm const *tmp)
+{
+  char const *ab = abbr(tmp);
+  if (HAVE_LOCALTIME_RZ)
+    return ab;
+  else {
+    size_t ablen = strlen(ab);
+    if (*bufalloc <= ablen) {
+      free(*buf);
+
+      /* Make the new buffer at least twice as long as the old,
+	 to avoid O(N**2) behavior on repeated calls.  */
+      *bufalloc = sumsize(*bufalloc, ablen + 1);
+
+      *buf = xmalloc(*bufalloc);
+    }
+    return strcpy(*buf, ab);
+  }
+}
+
+static void
+close_file(FILE *stream)
+{
+  char const *e = (ferror(stream) ? _("I/O error")
+		   : fclose(stream) != 0 ? strerror(errno) : NULL);
+  if (e) {
+    fprintf(stderr, "%s: %s\n", progname, e);
+    exit(EXIT_FAILURE);
+  }
 }
 
 static void
-usage(stream, status)
-FILE * const	stream;
-const int	status;
+usage(FILE * const stream, const int status)
 {
-	(void) fprintf(stream,
-_("%s: usage is %s [ --version ] [ --help ] [ -v ] [ -c [loyear,]hiyear ] zonename ...\n\
-\n\
-Report bugs to tz@elsie.nci.nih.gov.\n"),
-		       progname, progname);
+	fprintf(stream,
+_("%s: usage: %s OPTIONS TIMEZONE ...\n"
+  "Options include:\n"
+  "  -c [L,]U   Start at year L (default -500), end before year U (default 2500)\n"
+  "  -t [L,]U   Start at time L, end before time U (in seconds since 1970)\n"
+  "  -i         List transitions briefly (format is experimental)\n" \
+  "  -v         List transitions verbosely\n"
+  "  -V         List transitions a bit less verbosely\n"
+  "  --help     Output this help\n"
+  "  --version  Output version info\n"
+  "\n"
+  "Report bugs to %s.\n"),
+		progname, progname, REPORT_BUGS_TO);
+	if (status == EXIT_SUCCESS)
+	  close_file(stream);
 	exit(status);
 }
 
 int
-main(argc, argv)
-int	argc;
-char *	argv[];
+main(int argc, char *argv[])
 {
+	/* These are static so that they're initially zero.  */
+	static char *		abbrev;
+	static size_t		abbrevsize;
+
 	register int		i;
-	register int		c;
-	register int		vflag;
+	register bool		vflag;
+	register bool		Vflag;
 	register char *		cutarg;
-	register long		cutloyear = ZDUMP_LO_YEAR;
-	register long		cuthiyear = ZDUMP_HI_YEAR;
+	register char *		cuttimes;
 	register time_t		cutlotime;
 	register time_t		cuthitime;
-	register char **	fakeenv;
 	time_t			now;
-	time_t			t;
-	time_t			newt;
-	struct tm		tm;
-	struct tm		newtm;
-	register struct tm *	tmp;
-	register struct tm *	newtmp;
+	bool iflag = false;
 
-	INITIALIZE(cutlotime);
-	INITIALIZE(cuthitime);
+	cutlotime = absolute_min_time;
+	cuthitime = absolute_max_time;
 #if HAVE_GETTEXT
-	(void) setlocale(LC_ALL, "");
-#ifdef TZ_DOMAINDIR
-	(void) bindtextdomain(TZ_DOMAIN, TZ_DOMAINDIR);
-#endif /* defined TEXTDOMAINDIR */
-	(void) textdomain(TZ_DOMAIN);
+	setlocale(LC_ALL, "");
+# ifdef TZ_DOMAINDIR
+	bindtextdomain(TZ_DOMAIN, TZ_DOMAINDIR);
+# endif /* defined TEXTDOMAINDIR */
+	textdomain(TZ_DOMAIN);
 #endif /* HAVE_GETTEXT */
 	progname = argv[0];
 	for (i = 1; i < argc; ++i)
 		if (strcmp(argv[i], "--version") == 0) {
-			(void) printf("%s\n", elsieid);
-			exit(EXIT_SUCCESS);
+			printf("zdump %s%s\n", PKGVERSION, TZVERSION);
+			return EXIT_SUCCESS;
 		} else if (strcmp(argv[i], "--help") == 0) {
 			usage(stdout, EXIT_SUCCESS);
 		}
-	vflag = 0;
-	cutarg = NULL;
-	while ((c = getopt(argc, argv, "c:v")) == 'c' || c == 'v')
-		if (c == 'v')
-			vflag = 1;
-		else	cutarg = optarg;
-	if ((c != EOF && c != -1) ||
-		(optind == argc - 1 && strcmp(argv[optind], "=") == 0)) {
-			usage(stderr, EXIT_FAILURE);
-	}
-	if (vflag) {
-		if (cutarg != NULL) {
-			long	lo;
-			long	hi;
-			char	dummy;
+	vflag = Vflag = false;
+	cutarg = cuttimes = NULL;
+	for (;;)
+	  switch (getopt(argc, argv, "c:it:vV")) {
+	  case 'c': cutarg = optarg; break;
+	  case 't': cuttimes = optarg; break;
+	  case 'i': iflag = true; break;
+	  case 'v': vflag = true; break;
+	  case 'V': Vflag = true; break;
+	  case -1:
+	    if (! (optind == argc - 1 && strcmp(argv[optind], "=") == 0))
+	      goto arg_processing_done;
+	    /* Fall through.  */
+	  default:
+	    usage(stderr, EXIT_FAILURE);
+	  }
+ arg_processing_done:;
 
-			if (sscanf(cutarg, "%ld%c", &hi, &dummy) == 1) {
+	if (iflag | vflag | Vflag) {
+		intmax_t	lo;
+		intmax_t	hi;
+		char *loend, *hiend;
+		register intmax_t cutloyear = ZDUMP_LO_YEAR;
+		register intmax_t cuthiyear = ZDUMP_HI_YEAR;
+		if (cutarg != NULL) {
+			lo = strtoimax(cutarg, &loend, 10);
+			if (cutarg != loend && !*loend) {
+				hi = lo;
+				cuthiyear = hi;
+			} else if (cutarg != loend && *loend == ','
+				   && (hi = strtoimax(loend + 1, &hiend, 10),
+				       loend + 1 != hiend && !*hiend)) {
+				cutloyear = lo;
 				cuthiyear = hi;
-			} else if (sscanf(cutarg, "%ld,%ld%c",
-				&lo, &hi, &dummy) == 2) {
-					cutloyear = lo;
-					cuthiyear = hi;
 			} else {
-(void) fprintf(stderr, _("%s: wild -c argument %s\n"),
+				fprintf(stderr, _("%s: wild -c argument %s\n"),
 					progname, cutarg);
-				exit(EXIT_FAILURE);
+				return EXIT_FAILURE;
 			}
 		}
-		setabsolutes();
-		cutlotime = yeartot(cutloyear);
-		cuthitime = yeartot(cuthiyear);
+		if (cutarg != NULL || cuttimes == NULL) {
+			cutlotime = yeartot(cutloyear);
+			cuthitime = yeartot(cuthiyear);
+		}
+		if (cuttimes != NULL) {
+			lo = strtoimax(cuttimes, &loend, 10);
+			if (cuttimes != loend && !*loend) {
+				hi = lo;
+				if (hi < cuthitime) {
+					if (hi < absolute_min_time + 1)
+					  hi = absolute_min_time + 1;
+					cuthitime = hi;
+				}
+			} else if (cuttimes != loend && *loend == ','
+				   && (hi = strtoimax(loend + 1, &hiend, 10),
+				       loend + 1 != hiend && !*hiend)) {
+				if (cutlotime < lo) {
+					if (absolute_max_time < lo)
+						lo = absolute_max_time;
+					cutlotime = lo;
+				}
+				if (hi < cuthitime) {
+					if (hi < absolute_min_time + 1)
+					  hi = absolute_min_time + 1;
+					cuthitime = hi;
+				}
+			} else {
+				fprintf(stderr,
+					_("%s: wild -t argument %s\n"),
+					progname, cuttimes);
+				return EXIT_FAILURE;
+			}
+		}
+	}
+	gmtzinit();
+	if (iflag | vflag | Vflag)
+	  now = 0;
+	else {
+	  now = time(NULL);
+	  now |= !now;
 	}
-	(void) time(&now);
 	longest = 0;
-	for (i = optind; i < argc; ++i)
-		if (strlen(argv[i]) > longest)
-			longest = strlen(argv[i]);
-	{
-		register int	from;
-		register int	to;
-
-		for (i = 0; environ[i] != NULL; ++i)
-			continue;
-		fakeenv = (char **) malloc((size_t) ((i + 2) *
-			sizeof *fakeenv));
-		if (fakeenv == NULL ||
-			(fakeenv[0] = (char *) malloc(longest + 4)) == NULL) {
-					(void) perror(progname);
-					exit(EXIT_FAILURE);
-		}
-		to = 0;
-		(void) strcpy(fakeenv[to++], "TZ=");
-		for (from = 0; environ[from] != NULL; ++from)
-			if (strncmp(environ[from], "TZ=", 3) != 0)
-				fakeenv[to++] = environ[from];
-		fakeenv[to] = NULL;
-		environ = fakeenv;
+	for (i = optind; i < argc; i++) {
+	  size_t arglen = strlen(argv[i]);
+	  if (longest < arglen)
+	    longest = min(arglen, INT_MAX);
 	}
-	for (i = optind; i < argc; ++i) {
-		static char	buf[MAX_STRING_LENGTH];
 
-		(void) strcpy(&fakeenv[0][3], argv[i]);
-		if (!vflag) {
-			show(argv[i], now, FALSE);
+	for (i = optind; i < argc; ++i) {
+		timezone_t tz = tzalloc(argv[i]);
+		char const *ab;
+		time_t t;
+		struct tm tm, newtm;
+		bool tm_ok;
+		if (!tz) {
+		  perror(argv[i]);
+		  return EXIT_FAILURE;
+		}
+		if (now) {
+			show(tz, argv[i], now, false);
+			tzfree(tz);
 			continue;
 		}
-		warned = FALSE;
+		warned = false;
 		t = absolute_min_time;
-		show(argv[i], t, TRUE);
-		t += SECSPERHOUR * HOURSPERDAY;
-		show(argv[i], t, TRUE);
-		if (t < cutlotime)
-			t = cutlotime;
-		tmp = my_localtime(&t);
-		if (tmp != NULL) {
-			tm = *tmp;
-			(void) strncpy(buf, abbr(&tm), (sizeof buf) - 1);
-		}
-		for ( ; ; ) {
-			if (t >= cuthitime || t >= cuthitime - SECSPERHOUR * 12)
-				break;
-			newt = t + SECSPERHOUR * 12;
-			newtmp = localtime(&newt);
-			if (newtmp != NULL)
-				newtm = *newtmp;
-			if ((tmp == NULL || newtmp == NULL) ? (tmp != newtmp) :
-				(delta(&newtm, &tm) != (newt - t) ||
-				newtm.tm_isdst != tm.tm_isdst ||
-				strcmp(abbr(&newtm), buf) != 0)) {
-					newt = hunt(argv[i], t, newt);
-					newtmp = localtime(&newt);
-					if (newtmp != NULL) {
-						newtm = *newtmp;
-						(void) strncpy(buf,
-							abbr(&newtm),
-							(sizeof buf) - 1);
-					}
+		if (! (iflag | Vflag)) {
+			show(tz, argv[i], t, true);
+			if (my_localtime_rz(tz, &t, &tm) == NULL
+			    && t < cutlotime) {
+				time_t newt = cutlotime;
+				if (my_localtime_rz(tz, &newt, &newtm) != NULL)
+				  showextrema(tz, argv[i], t, NULL, newt);
 			}
-			t = newt;
-			tm = newtm;
-			tmp = newtmp;
 		}
-		t = absolute_max_time;
-		t -= SECSPERHOUR * HOURSPERDAY;
-		show(argv[i], t, TRUE);
-		t += SECSPERHOUR * HOURSPERDAY;
-		show(argv[i], t, TRUE);
-	}
-	if (fflush(stdout) || ferror(stdout)) {
-		(void) fprintf(stderr, "%s: ", progname);
-		(void) perror(_("Error writing to standard output"));
-		exit(EXIT_FAILURE);
-	}
-	exit(EXIT_SUCCESS);
-	/* If exit fails to exit... */
-	return EXIT_FAILURE;
-}
-
-static void
-setabsolutes(void)
-{
-	if (0.5 == (time_t) 0.5) {
-		/*
-		** time_t is floating.
-		*/
-		if (sizeof (time_t) == sizeof (float)) {
-			absolute_min_time = (time_t) -FLT_MAX;
-			absolute_max_time = (time_t) FLT_MAX;
-		} else if (sizeof (time_t) == sizeof (double)) {
-			absolute_min_time = (time_t) -DBL_MAX;
-			absolute_max_time = (time_t) DBL_MAX;
-		} else {
-			(void) fprintf(stderr,
-_("%s: use of -v on system with floating time_t other than float or double\n"),
-				progname);
-			exit(EXIT_FAILURE);
+		if (t + 1 < cutlotime)
+		  t = cutlotime - 1;
+		tm_ok = my_localtime_rz(tz, &t, &tm) != NULL;
+		if (tm_ok) {
+		  ab = saveabbr(&abbrev, &abbrevsize, &tm);
+		  if (iflag) {
+		    showtrans("\nTZ=%f", &tm, t, ab, argv[i]);
+		    showtrans("-\t-\t%Q", &tm, t, ab, argv[i]);
+		  }
+		} else
+		  ab = NULL;
+		while (t < cuthitime - 1) {
+		  time_t newt = ((t < absolute_max_time - SECSPERDAY / 2
+				  && t + SECSPERDAY / 2 < cuthitime - 1)
+				 ? t + SECSPERDAY / 2
+				 : cuthitime - 1);
+		  struct tm *newtmp = localtime_rz(tz, &newt, &newtm);
+		  bool newtm_ok = newtmp != NULL;
+		  if (tm_ok != newtm_ok
+		      || (ab && (delta(&newtm, &tm) != newt - t
+				 || newtm.tm_isdst != tm.tm_isdst
+				 || strcmp(abbr(&newtm), ab) != 0))) {
+		    newt = hunt(tz, argv[i], t, newt, false);
+		    newtmp = localtime_rz(tz, &newt, &newtm);
+		    newtm_ok = newtmp != NULL;
+		    if (iflag)
+		      showtrans("%Y-%m-%d\t%L\t%Q", newtmp, newt,
+				newtm_ok ? abbr(&newtm) : NULL, argv[i]);
+		    else {
+		      show(tz, argv[i], newt - 1, true);
+		      show(tz, argv[i], newt, true);
+		    }
+		  }
+		  t = newt;
+		  tm_ok = newtm_ok;
+		  if (newtm_ok) {
+		    ab = saveabbr(&abbrev, &abbrevsize, &newtm);
+		    tm = newtm;
+		  }
 		}
-	} else if (0 > (time_t) -1) {
-		/*
-		** time_t is signed.  Assume overflow wraps around.
-		*/
-		time_t t = 0;
-		time_t t1 = 1;
-
-		while (t < t1) {
-			t = t1;
-			t1 = 2 * t1 + 1;
+		if (! (iflag | Vflag)) {
+			time_t newt = absolute_max_time;
+			t = cuthitime;
+			if (t < newt) {
+			  struct tm *tmp = my_localtime_rz(tz, &t, &tm);
+			  if (tmp != NULL
+			      && my_localtime_rz(tz, &newt, &newtm) == NULL)
+			    showextrema(tz, argv[i], t, tmp, newt);
+			}
+			show(tz, argv[i], absolute_max_time, true);
 		}
-
-		absolute_max_time = t;
-		t = -t;
-		absolute_min_time = t - 1;
-		if (t < absolute_min_time)
-			absolute_min_time = t;
-	} else {
-		/*
-		** time_t is unsigned.
-		*/
-		absolute_min_time = 0;
-		absolute_max_time = absolute_min_time - 1;
+		tzfree(tz);
 	}
+	close_file(stdout);
+	if (errout && (ferror(stderr) || fclose(stderr) != 0))
+	  return EXIT_FAILURE;
+	return EXIT_SUCCESS;
 }
 
 static time_t
-yeartot(y)
-const long	y;
+yeartot(intmax_t y)
 {
-	register long	myy;
-	register long	seconds;
-	register time_t	t;
+	register intmax_t	myy, seconds, years;
+	register time_t		t;
 
 	myy = EPOCH_YEAR;
 	t = 0;
-	while (myy != y) {
-		if (myy < y) {
+	while (myy < y) {
+		if (SECSPER400YEARS_FITS && 400 <= y - myy) {
+			intmax_t diff400 = (y - myy) / 400;
+			if (INTMAX_MAX / SECSPER400YEARS < diff400)
+				return absolute_max_time;
+			seconds = diff400 * SECSPER400YEARS;
+			years = diff400 * 400;
+                } else {
 			seconds = isleap(myy) ? SECSPERLYEAR : SECSPERNYEAR;
-			++myy;
-			if (t > absolute_max_time - seconds) {
-				t = absolute_max_time;
-				break;
-			}
-			t += seconds;
+			years = 1;
+		}
+		myy += years;
+		if (t > absolute_max_time - seconds)
+			return absolute_max_time;
+		t += seconds;
+	}
+	while (y < myy) {
+		if (SECSPER400YEARS_FITS && y + 400 <= myy && myy < 0) {
+			intmax_t diff400 = (myy - y) / 400;
+			if (INTMAX_MAX / SECSPER400YEARS < diff400)
+				return absolute_min_time;
+			seconds = diff400 * SECSPER400YEARS;
+			years = diff400 * 400;
 		} else {
-			--myy;
-			seconds = isleap(myy) ? SECSPERLYEAR : SECSPERNYEAR;
-			if (t < absolute_min_time + seconds) {
-				t = absolute_min_time;
-				break;
-			}
-			t -= seconds;
+			seconds = isleap(myy - 1) ? SECSPERLYEAR : SECSPERNYEAR;
+			years = 1;
 		}
+		myy -= years;
+		if (t < absolute_min_time + seconds)
+			return absolute_min_time;
+		t -= seconds;
 	}
 	return t;
 }
 
+/* Search for a discontinuity in timezone TZ with name NAME, in the
+   timestamps ranging from LOT through HIT.  LOT and HIT disagree
+   about some aspect of timezone.  If ONLY_OK, search only for
+   definedness changes, i.e., localtime succeeds on one side of the
+   transition but fails on the other side.  Return the timestamp just
+   before the transition from LOT's settings.  */
+
 static time_t
-hunt(char *name, time_t lot, time_t hit)
+hunt(timezone_t tz, char *name, time_t lot, time_t hit, bool only_ok)
 {
-	time_t			t;
-	long			diff;
+	static char *		loab;
+	static size_t		loabsize;
 	struct tm		lotm;
-	register struct tm *	lotmp;
 	struct tm		tm;
-	register struct tm *	tmp;
-	char			loab[MAX_STRING_LENGTH];
 
-	lotmp = my_localtime(&lot);
-	if (lotmp != NULL) {
-		lotm = *lotmp;
-		(void) strncpy(loab, abbr(&lotm), (sizeof loab) - 1);
-	}
+	/* Convert LOT into a broken-down time here, even though our
+	   caller already did that.  On platforms without TM_ZONE,
+	   tzname may have been altered since our caller broke down
+	   LOT, and tzname needs to be changed back.  */
+	bool lotm_ok = my_localtime_rz(tz, &lot, &lotm) != NULL;
+	bool tm_ok;
+	char const *ab = lotm_ok ? saveabbr(&loab, &loabsize, &lotm) : NULL;
+
 	for ( ; ; ) {
-		diff = (long) (hit - lot);
-		if (diff < 2)
+		/* T = average of LOT and HIT, rounding down.
+		   Avoid overflow, even on oddball C89 platforms
+		   where / rounds down and TIME_T_MIN == -TIME_T_MAX
+		   so lot / 2 + hit / 2 might overflow.  */
+		time_t t = (lot / 2
+			    - ((lot % 2 + hit % 2) < 0)
+			    + ((lot % 2 + hit % 2) == 2)
+			    + hit / 2);
+		if (t == lot)
 			break;
-		t = lot;
-		t += diff / 2;
-		if (t <= lot)
-			++t;
-		else if (t >= hit)
-			--t;
-		tmp = my_localtime(&t);
-		if (tmp != NULL)
-			tm = *tmp;
-		if ((lotmp == NULL || tmp == NULL) ? (lotmp == tmp) :
-			(delta(&tm, &lotm) == (t - lot) &&
-			tm.tm_isdst == lotm.tm_isdst &&
-			strcmp(abbr(&tm), loab) == 0)) {
-				lot = t;
-				lotm = tm;
-				lotmp = tmp;
+		tm_ok = my_localtime_rz(tz, &t, &tm) != NULL;
+		if (lotm_ok == tm_ok
+		    && (only_ok
+			|| (ab && tm.tm_isdst == lotm.tm_isdst
+			    && delta(&tm, &lotm) == t - lot
+			    && strcmp(abbr(&tm), ab) == 0))) {
+		  lot = t;
+		  if (tm_ok)
+		    lotm = tm;
 		} else	hit = t;
 	}
-	show(name, lot, TRUE);
-	show(name, hit, TRUE);
 	return hit;
 }
 
 /*
-** Thanks to Paul Eggert for logic used in delta.
+** Thanks to Paul Eggert for logic used in delta_nonneg.
 */
 
-static long
-delta(newp, oldp)
-struct tm *	newp;
-struct tm *	oldp;
+static intmax_t
+delta_nonneg(struct tm *newp, struct tm *oldp)
 {
-	register long	result;
-	register int	tmy;
-
-	if (newp->tm_year < oldp->tm_year)
-		return -delta(oldp, newp);
-	result = 0;
-	for (tmy = oldp->tm_year; tmy < newp->tm_year; ++tmy)
+	intmax_t oldy = oldp->tm_year;
+	int cycles = (newp->tm_year - oldy) / YEARSPERREPEAT;
+	intmax_t sec = SECSPERREPEAT, result = cycles * sec;
+	int tmy = oldp->tm_year + cycles * YEARSPERREPEAT;
+	for ( ; tmy < newp->tm_year; ++tmy)
 		result += DAYSPERNYEAR + isleap_sum(tmy, TM_YEAR_BASE);
 	result += newp->tm_yday - oldp->tm_yday;
 	result *= HOURSPERDAY;
@@ -552,117 +750,465 @@ struct tm *	oldp;
 	return result;
 }
 
+static intmax_t
+delta(struct tm *newp, struct tm *oldp)
+{
+  return (newp->tm_year < oldp->tm_year
+	  ? -delta_nonneg(oldp, newp)
+	  : delta_nonneg(newp, oldp));
+}
+
+#ifndef TM_GMTOFF
+/* Return A->tm_yday, adjusted to compare it fairly to B->tm_yday.
+   Assume A and B differ by at most one year.  */
+static int
+adjusted_yday(struct tm const *a, struct tm const *b)
+{
+  int yday = a->tm_yday;
+  if (b->tm_year < a->tm_year)
+    yday += 365 + isleap_sum(b->tm_year, TM_YEAR_BASE);
+  return yday;
+}
+#endif
+
+/* If A is the broken-down local time and B the broken-down UT for
+   the same instant, return A's UT offset in seconds, where positive
+   offsets are east of Greenwich.  On failure, return LONG_MIN.
+
+   If T is nonnull, *T is the timestamp that corresponds to A; call
+   my_gmtime_r and use its result instead of B.  Otherwise, B is the
+   possibly nonnull result of an earlier call to my_gmtime_r.  */
+static long
+gmtoff(struct tm const *a, time_t *t, struct tm const *b)
+{
+#ifdef TM_GMTOFF
+  return a->TM_GMTOFF;
+#else
+  struct tm tm;
+  if (t)
+    b = my_gmtime_r(t, &tm);
+  if (! b)
+    return LONG_MIN;
+  else {
+    int ayday = adjusted_yday(a, b);
+    int byday = adjusted_yday(b, a);
+    int days = ayday - byday;
+    long hours = a->tm_hour - b->tm_hour + 24 * days;
+    long minutes = a->tm_min - b->tm_min + 60 * hours;
+    long seconds = a->tm_sec - b->tm_sec + 60 * minutes;
+    return seconds;
+  }
+#endif
+}
+
 static void
-show(char *zone, time_t t, int v)
+show(timezone_t tz, char *zone, time_t t, bool v)
 {
 	register struct tm *	tmp;
+	register struct tm *	gmtmp;
+	struct tm tm, gmtm;
 
-	(void) printf("%-*s  ", (int) longest, zone);
+	printf("%-*s  ", longest, zone);
 	if (v) {
-		tmp = gmtime(&t);
-		if (tmp == NULL) {
-			(void) printf(tformat(), t);
+		gmtmp = my_gmtime_r(&t, &gmtm);
+		if (gmtmp == NULL) {
+			printf(tformat(), t);
+			printf(_(" (gmtime failed)"));
 		} else {
-			dumptime(tmp);
-			(void) printf(" UTC");
+			dumptime(gmtmp);
+			printf(" UT");
 		}
-		(void) printf(" = ");
+		printf(" = ");
 	}
-	tmp = my_localtime(&t);
-	dumptime(tmp);
-	if (tmp != NULL) {
+	tmp = my_localtime_rz(tz, &t, &tm);
+	if (tmp == NULL) {
+		printf(tformat(), t);
+		printf(_(" (localtime failed)"));
+	} else {
+		dumptime(tmp);
 		if (*abbr(tmp) != '\0')
-			(void) printf(" %s", abbr(tmp));
+			printf(" %s", abbr(tmp));
 		if (v) {
-			(void) printf(" isdst=%d", tmp->tm_isdst);
-#ifdef TM_GMTOFF
-			(void) printf(" gmtoff=%ld", tmp->TM_GMTOFF);
-#endif /* defined TM_GMTOFF */
+			long off = gmtoff(tmp, NULL, gmtmp);
+			printf(" isdst=%d", tmp->tm_isdst);
+			if (off != LONG_MIN)
+			  printf(" gmtoff=%ld", off);
 		}
 	}
-	(void) printf("\n");
+	printf("\n");
 	if (tmp != NULL && *abbr(tmp) != '\0')
 		abbrok(abbr(tmp), zone);
 }
 
-static char *
-abbr(tmp)
-struct tm *	tmp;
+/* Show timestamps just before and just after a transition between
+   defined and undefined (or vice versa) in either localtime or
+   gmtime.  These transitions are for timezone TZ with name ZONE, in
+   the range from LO (with broken-down time LOTMP if that is nonnull)
+   through HI.  LO and HI disagree on definedness.  */
+
+static void
+showextrema(timezone_t tz, char *zone, time_t lo, struct tm *lotmp, time_t hi)
+{
+  struct tm localtm[2], gmtm[2];
+  time_t t, boundary = hunt(tz, zone, lo, hi, true);
+  bool old = false;
+  hi = (SECSPERDAY < hi - boundary
+	? boundary + SECSPERDAY
+	: hi + (hi < TIME_T_MAX));
+  if (SECSPERDAY < boundary - lo) {
+    lo = boundary - SECSPERDAY;
+    lotmp = my_localtime_rz(tz, &lo, &localtm[old]);
+  }
+  if (lotmp)
+    localtm[old] = *lotmp;
+  else
+    localtm[old].tm_sec = -1;
+  if (! my_gmtime_r(&lo, &gmtm[old]))
+    gmtm[old].tm_sec = -1;
+
+  /* Search sequentially for definedness transitions.  Although this
+     could be sped up by refining 'hunt' to search for either
+     localtime or gmtime definedness transitions, it hardly seems
+     worth the trouble.  */
+  for (t = lo + 1; t < hi; t++) {
+    bool new = !old;
+    if (! my_localtime_rz(tz, &t, &localtm[new]))
+      localtm[new].tm_sec = -1;
+    if (! my_gmtime_r(&t, &gmtm[new]))
+      gmtm[new].tm_sec = -1;
+    if (((localtm[old].tm_sec < 0) != (localtm[new].tm_sec < 0))
+	| ((gmtm[old].tm_sec < 0) != (gmtm[new].tm_sec < 0))) {
+      show(tz, zone, t - 1, true);
+      show(tz, zone, t, true);
+    }
+    old = new;
+  }
+}
+
+#if HAVE_SNPRINTF
+# define my_snprintf snprintf
+#else
+# include <stdarg.h>
+
+/* A substitute for snprintf that is good enough for zdump.  */
+static int ATTRIBUTE_FORMAT((printf, 3, 4))
+my_snprintf(char *s, size_t size, char const *format, ...)
+{
+  int n;
+  va_list args;
+  char const *arg;
+  size_t arglen, slen;
+  char buf[1024];
+  va_start(args, format);
+  if (strcmp(format, "%s") == 0) {
+    arg = va_arg(args, char const *);
+    arglen = strlen(arg);
+  } else {
+    n = vsprintf(buf, format, args);
+    if (n < 0) {
+      va_end(args);
+      return n;
+    }
+    arg = buf;
+    arglen = n;
+  }
+  slen = arglen < size ? arglen : size - 1;
+  memcpy(s, arg, slen);
+  s[slen] = '\0';
+  n = arglen <= INT_MAX ? arglen : -1;
+  va_end(args);
+  return n;
+}
+#endif
+
+/* Store into BUF, of size SIZE, a formatted local time taken from *TM.
+   Use ISO 8601 format +HH:MM:SS.  Omit :SS if SS is zero, and omit
+   :MM too if MM is also zero.
+
+   Return the length of the resulting string.  If the string does not
+   fit, return the length that the string would have been if it had
+   fit; do not overrun the output buffer.  */
+static int
+format_local_time(char *buf, size_t size, struct tm const *tm)
+{
+  int ss = tm->tm_sec, mm = tm->tm_min, hh = tm->tm_hour;
+  return (ss
+	  ? my_snprintf(buf, size, "%02d:%02d:%02d", hh, mm, ss)
+	  : mm
+	  ? my_snprintf(buf, size, "%02d:%02d", hh, mm)
+	  : my_snprintf(buf, size, "%02d", hh));
+}
+
+/* Store into BUF, of size SIZE, a formatted UT offset for the
+   localtime *TM corresponding to time T.  Use ISO 8601 format
+   +HHMMSS, or -HHMMSS for timestamps west of Greenwich; use the
+   format -00 for unknown UT offsets.  If the hour needs more than
+   two digits to represent, extend the length of HH as needed.
+   Otherwise, omit SS if SS is zero, and omit MM too if MM is also
+   zero.
+
+   Return the length of the resulting string, or -1 if the result is
+   not representable as a string.  If the string does not fit, return
+   the length that the string would have been if it had fit; do not
+   overrun the output buffer.  */
+static int
+format_utc_offset(char *buf, size_t size, struct tm const *tm, time_t t)
+{
+  long off = gmtoff(tm, &t, NULL);
+  char sign = ((off < 0
+		|| (off == 0
+		    && (*abbr(tm) == '-' || strcmp(abbr(tm), "zzz") == 0)))
+	       ? '-' : '+');
+  long hh;
+  int mm, ss;
+  if (off < 0)
+    {
+      if (off == LONG_MIN)
+	return -1;
+      off = -off;
+    }
+  ss = off % 60;
+  mm = off / 60 % 60;
+  hh = off / 60 / 60;
+  return (ss || 100 <= hh
+	  ? my_snprintf(buf, size, "%c%02ld%02d%02d", sign, hh, mm, ss)
+	  : mm
+	  ? my_snprintf(buf, size, "%c%02ld%02d", sign, hh, mm)
+	  : my_snprintf(buf, size, "%c%02ld", sign, hh));
+}
+
+/* Store into BUF (of size SIZE) a quoted string representation of P.
+   If the representation's length is less than SIZE, return the
+   length; the representation is not null terminated.  Otherwise
+   return SIZE, to indicate that BUF is too small.  */
+static size_t
+format_quoted_string(char *buf, size_t size, char const *p)
+{
+  char *b = buf;
+  size_t s = size;
+  if (!s)
+    return size;
+  *b++ = '"', s--;
+  for (;;) {
+    char c = *p++;
+    if (s <= 1)
+      return size;
+    switch (c) {
+    default: *b++ = c, s--; continue;
+    case '\0': *b++ = '"', s--; return size - s;
+    case '"': case '\\': break;
+    case ' ': c = 's'; break;
+    case '\f': c = 'f'; break;
+    case '\n': c = 'n'; break;
+    case '\r': c = 'r'; break;
+    case '\t': c = 't'; break;
+    case '\v': c = 'v'; break;
+    }
+    *b++ = '\\', *b++ = c, s -= 2;
+  }
+}
+
+/* Store into BUF (of size SIZE) a timestamp formatted by TIME_FMT.
+   TM is the broken-down time, T the seconds count, AB the time zone
+   abbreviation, and ZONE_NAME the zone name.  Return true if
+   successful, false if the output would require more than SIZE bytes.
+   TIME_FMT uses the same format that strftime uses, with these
+   additions:
+
+   %f zone name
+   %L local time as per format_local_time
+   %Q like "U\t%Z\tD" where U is the UT offset as for format_utc_offset
+      and D is the isdst flag; except omit D if it is zero, omit %Z if
+      it equals U, quote and escape %Z if it contains nonalphabetics,
+      and omit any trailing tabs.  */
+
+static bool
+istrftime(char *buf, size_t size, char const *time_fmt,
+	  struct tm const *tm, time_t t, char const *ab, char const *zone_name)
+{
+  char *b = buf;
+  size_t s = size;
+  char const *f = time_fmt, *p;
+
+  for (p = f; ; p++)
+    if (*p == '%' && p[1] == '%')
+      p++;
+    else if (!*p
+	     || (*p == '%'
+		 && (p[1] == 'f' || p[1] == 'L' || p[1] == 'Q'))) {
+      size_t formatted_len;
+      size_t f_prefix_len = p - f;
+      size_t f_prefix_copy_size = p - f + 2;
+      char fbuf[100];
+      bool oversized = sizeof fbuf <= f_prefix_copy_size;
+      char *f_prefix_copy = oversized ? xmalloc(f_prefix_copy_size) : fbuf;
+      memcpy(f_prefix_copy, f, f_prefix_len);
+      strcpy(f_prefix_copy + f_prefix_len, "X");
+      formatted_len = strftime(b, s, f_prefix_copy, tm);
+      if (oversized)
+	free(f_prefix_copy);
+      if (formatted_len == 0)
+	return false;
+      formatted_len--;
+      b += formatted_len, s -= formatted_len;
+      if (!*p++)
+	break;
+      switch (*p) {
+      case 'f':
+	formatted_len = format_quoted_string(b, s, zone_name);
+	break;
+      case 'L':
+	formatted_len = format_local_time(b, s, tm);
+	break;
+      case 'Q':
+	{
+	  bool show_abbr;
+	  int offlen = format_utc_offset(b, s, tm, t);
+	  if (! (0 <= offlen && offlen < s))
+	    return false;
+	  show_abbr = strcmp(b, ab) != 0;
+	  b += offlen, s -= offlen;
+	  if (show_abbr) {
+	    char const *abp;
+	    size_t len;
+	    if (s <= 1)
+	      return false;
+	    *b++ = '\t', s--;
+	    for (abp = ab; is_alpha(*abp); abp++)
+	      continue;
+	    len = (!*abp && *ab
+		   ? my_snprintf(b, s, "%s", ab)
+		   : format_quoted_string(b, s, ab));
+	    if (s <= len)
+	      return false;
+	    b += len, s -= len;
+	  }
+	  formatted_len
+	    = (tm->tm_isdst
+	       ? my_snprintf(b, s, &"\t\t%d"[show_abbr], tm->tm_isdst)
+	       : 0);
+	}
+	break;
+      }
+      if (s <= formatted_len)
+	return false;
+      b += formatted_len, s -= formatted_len;
+      f = p + 1;
+    }
+  *b = '\0';
+  return true;
+}
+
+/* Show a time transition.  */
+static void
+showtrans(char const *time_fmt, struct tm const *tm, time_t t, char const *ab,
+	  char const *zone_name)
 {
-	register char *	result;
-	static char	nada;
+  if (!tm) {
+    printf(tformat(), t);
+    putchar('\n');
+  } else {
+    char stackbuf[1000];
+    size_t size = sizeof stackbuf;
+    char *buf = stackbuf;
+    char *bufalloc = NULL;
+    while (! istrftime(buf, size, time_fmt, tm, t, ab, zone_name)) {
+      size = sumsize(size, size);
+      free(bufalloc);
+      buf = bufalloc = xmalloc(size);
+    }
+    puts(buf);
+    free(bufalloc);
+  }
+}
 
-	if (tmp->tm_isdst != 0 && tmp->tm_isdst != 1)
-		return &nada;
-	result = tzname[tmp->tm_isdst];
-	return (result == NULL) ? &nada : result;
+static char const *
+abbr(struct tm const *tmp)
+{
+#ifdef TM_ZONE
+	return tmp->TM_ZONE;
+#else
+# if HAVE_TZNAME
+	if (0 <= tmp->tm_isdst && tzname[0 < tmp->tm_isdst])
+	  return tzname[0 < tmp->tm_isdst];
+# endif
+	return "";
+#endif
 }
 
 /*
 ** The code below can fail on certain theoretical systems;
-** it works on all known real-world systems as of 2004-12-30.
+** it works on all known real-world systems as of 2022-01-25.
 */
 
 static const char *
 tformat(void)
 {
-	if (0.5 == (time_t) 0.5) {	/* floating */
-		if (sizeof (time_t) > sizeof (double))
-			return "%Lg";
-		return "%g";
-	}
+#if HAVE_GENERIC
+	/* C11-style _Generic is more likely to return the correct
+	   format when distinct types have the same size.  */
+	char const *fmt =
+	  _Generic(+ (time_t) 0,
+		   int: "%d", long: "%ld", long long: "%lld",
+		   unsigned: "%u", unsigned long: "%lu",
+		   unsigned long long: "%llu",
+		   default: NULL);
+	if (fmt)
+	  return fmt;
+	fmt = _Generic((time_t) 0,
+		       intmax_t: "%"PRIdMAX, uintmax_t: "%"PRIuMAX,
+		       default: NULL);
+	if (fmt)
+	  return fmt;
+#endif
 	if (0 > (time_t) -1) {		/* signed */
-		if (sizeof (time_t) > sizeof (long))
+		if (sizeof(time_t) == sizeof(intmax_t))
+			return "%"PRIdMAX;
+		if (sizeof(time_t) > sizeof(long))
 			return "%lld";
-		if (sizeof (time_t) > sizeof (int))
+		if (sizeof(time_t) > sizeof(int))
 			return "%ld";
 		return "%d";
 	}
-	if (sizeof (time_t) > sizeof (unsigned long))
+#ifdef PRIuMAX
+	if (sizeof(time_t) == sizeof(uintmax_t))
+		return "%"PRIuMAX;
+#endif
+	if (sizeof(time_t) > sizeof(unsigned long))
 		return "%llu";
-	if (sizeof (time_t) > sizeof (unsigned int))
+	if (sizeof(time_t) > sizeof(unsigned int))
 		return "%lu";
 	return "%u";
 }
 
 static void
-dumptime(timeptr)
-register const struct tm *	timeptr;
+dumptime(register const struct tm *timeptr)
 {
-	static const char	wday_name[][3] = {
+	static const char	wday_name[][4] = {
 		"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
 	};
-	static const char	mon_name[][3] = {
+	static const char	mon_name[][4] = {
 		"Jan", "Feb", "Mar", "Apr", "May", "Jun",
 		"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
 	};
-	register const char *	wn;
-	register const char *	mn;
 	register int		lead;
 	register int		trail;
+	int DIVISOR = 10;
 
-	if (timeptr == NULL) {
-		(void) printf("NULL");
-		return;
-	}
 	/*
-	** The packaged versions of localtime and gmtime never put out-of-range
+	** The packaged localtime_rz and gmtime_r never put out-of-range
 	** values in tm_wday or tm_mon, but since this code might be compiled
 	** with other (perhaps experimental) versions, paranoia is in order.
 	*/
-	if (timeptr->tm_wday < 0 || timeptr->tm_wday >=
-		(int) (sizeof wday_name / sizeof wday_name[0]))
-			wn = "???";
-	else		wn = wday_name[timeptr->tm_wday];
-	if (timeptr->tm_mon < 0 || timeptr->tm_mon >=
-		(int) (sizeof mon_name / sizeof mon_name[0]))
-			mn = "???";
-	else		mn = mon_name[timeptr->tm_mon];
-	(void) printf("%.3s %.3s%3d %.2d:%.2d:%.2d ",
-		wn, mn,
+	printf("%s %s%3d %.2d:%.2d:%.2d ",
+		((0 <= timeptr->tm_wday
+		  && timeptr->tm_wday < sizeof wday_name / sizeof wday_name[0])
+		 ? wday_name[timeptr->tm_wday] : "???"),
+		((0 <= timeptr->tm_mon
+		  && timeptr->tm_mon < sizeof mon_name / sizeof mon_name[0])
+		 ? mon_name[timeptr->tm_mon] : "???"),
 		timeptr->tm_mday, timeptr->tm_hour,
 		timeptr->tm_min, timeptr->tm_sec);
-#define DIVISOR	10
 	trail = timeptr->tm_year % DIVISOR + TM_YEAR_BASE % DIVISOR;
 	lead = timeptr->tm_year / DIVISOR + TM_YEAR_BASE / DIVISOR +
 		trail / DIVISOR;
@@ -675,6 +1221,6 @@ register const struct tm *	timeptr;
 		++lead;
 	}
 	if (lead == 0)
-		(void) printf("%d", trail);
-	else	(void) printf("%d%d", lead, ((trail < 0) ? -trail : trail));
+		printf("%d", trail);
+	else	printf("%d%d", lead, ((trail < 0) ? -trail : trail));
 }